U.S. patent number 10,968,528 [Application Number 16/619,234] was granted by the patent office on 2021-04-06 for steel sheet for cans, and production method therefor.
This patent grant is currently assigned to JFE STEEL CORPORATION. The grantee listed for this patent is JFE STEEL CORPORATION. Invention is credited to Yuya Baba, Katsumi Kojima, Yusuke Nakagawa, Hanyou Sou, Mikito Suto, Takeshi Suzuki, Shunsuke Tokui, Yoichiro Yamanaka.
![](/patent/grant/10968528/US10968528-20210406-D00000.png)
![](/patent/grant/10968528/US10968528-20210406-D00001.png)
United States Patent |
10,968,528 |
Nakagawa , et al. |
April 6, 2021 |
Steel sheet for cans, and production method therefor
Abstract
A steel sheet for cans which exhibits excellent weldability; and
a production method therefore include the surface of a steel sheet
in order from the steel sheet side, a chromium metal layer and a
hydrous chromium oxide layer. The deposited amount of the chromium
metal layer is 50-200 mg/m.sup.2. The deposited amount of the
hydrous chromium oxide layer in terms of chromium is 3-30
mg/m.sup.2. The chromium metal layer includes: a base part having a
thickness of 7.0 nm or higher; and granular protrusions which are
on the base part, have a maximum grain size of 200 nm or lower, and
have a number density per unit area of at least 30 per
.mu.m.sup.2.
Inventors: |
Nakagawa; Yusuke (Tokyo,
JP), Suzuki; Takeshi (Tokyo, JP), Suto;
Mikito (Tokyo, JP), Kojima; Katsumi (Tokyo,
JP), Baba; Yuya (Tokyo, JP), Sou;
Hanyou (Tokyo, JP), Yamanaka; Yoichiro (Tokyo,
JP), Tokui; Shunsuke (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JFE STEEL CORPORATION |
Tokyo |
N/A |
JP |
|
|
Assignee: |
JFE STEEL CORPORATION (Tokyo,
JP)
|
Family
ID: |
1000005468664 |
Appl.
No.: |
16/619,234 |
Filed: |
June 5, 2018 |
PCT
Filed: |
June 05, 2018 |
PCT No.: |
PCT/JP2018/021570 |
371(c)(1),(2),(4) Date: |
December 04, 2019 |
PCT
Pub. No.: |
WO2018/225739 |
PCT
Pub. Date: |
December 13, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200149179 A1 |
May 14, 2020 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 9, 2017 [JP] |
|
|
JP2017-114530 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D
7/00 (20130101); C25D 11/38 (20130101); C25D
5/18 (20130101); C25D 5/16 (20130101); C23C
28/32 (20130101) |
Current International
Class: |
C25D
11/38 (20060101); C25D 5/18 (20060101); C25D
7/00 (20060101); C25D 5/16 (20060101); C23C
28/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
86102555 |
|
Dec 1986 |
|
CN |
|
106133206 |
|
Nov 2016 |
|
CN |
|
108368615 |
|
Aug 2018 |
|
CN |
|
108368616 |
|
Aug 2018 |
|
CN |
|
S61-281899 |
|
Dec 1986 |
|
JP |
|
S63-186894 |
|
Aug 1988 |
|
JP |
|
H01-096397 |
|
Apr 1989 |
|
JP |
|
H03-177599 |
|
Aug 1991 |
|
JP |
|
H03-229897 |
|
Oct 1991 |
|
JP |
|
H04-187797 |
|
Jul 1992 |
|
JP |
|
H05-287591 |
|
Nov 1993 |
|
JP |
|
H11-189898 |
|
Jul 1999 |
|
JP |
|
2017/098991 |
|
Jun 2017 |
|
WO |
|
2017/098994 |
|
Jun 2017 |
|
WO |
|
Other References
Jan. 9, 2019 Taiwanese Office Action issued in Taiwanese Patent
Application No. 107119744. cited by applicant .
May 28, 2019 Japanese Office Action issued in Japanese Patent
Application No. 2018-549599. cited by applicant .
Sep. 10, 2019 Japanese Office Action issued in Japanese Patent
Application No. 2018-549599. cited by applicant .
Aug. 28, 2018 International Search Report issued in International
Patent Application No. PCT/JP2018/021570. cited by applicant .
Mar. 26, 2020 Office Action issued in U.S. Appl. No. 16/061,079.
cited by applicant .
May 25, 2020 Extended European Search Report issued in European
Patent Application No. 18812947.2. cited by applicant .
Aug. 21, 2020 Office Action issued in U.S. Appl. No. 16/060,206.
cited by applicant .
Aug. 28, 2020 Office Action issued in Australian Application No.
2018280968. cited by applicant .
Feb. 5, 2021 Office Action issued in Chinese Patent Application No.
201880037191.5. cited by applicant.
|
Primary Examiner: Schleis; Daniel J.
Attorney, Agent or Firm: Oliff PLC
Claims
The invention claimed is:
1. A tin mill black plate comprising, on a surface of a steel
sheet, a chromium metal layer and a hydrated chromium oxide layer
stacked in this order from a steel sheet side, wherein the chromium
metal layer has a coating weight of 50 to 200 mg/m.sup.2, wherein
the hydrated chromium oxide layer has a coating weight of 3 to 30
mg/m.sup.2 in terms of chromium amount, and wherein the chromium
metal layer includes a base portion with a thickness of not less
than 7.0 nm and granular protrusions provided on the base portion
and having a maximum diameter of not more than 200 nm and a number
density per unit area of not less than 30
protrusions/.mu.m.sup.2.
2. The tin mill black plate according to claim 1, wherein the
hydrated chromium oxide layer has a coating weight of more than 15
mg/m.sup.2 but not more than 30 mg/m.sup.2 in terms of chromium
amount.
3. The tin mill black plate according to claim 1, wherein the
granular protrusions have a number density per unit area of not
less than 200 protrusions/.mu.m.sup.2.
4. The tin mill black plate according to claim 2, wherein the
granular protrusions have a number density per unit area of not
less than 200 protrusions/.mu.m.sup.2.
5. A tin mill black plate manufacturing method for obtaining the
tin mill black plate according to claim 1 by use of an aqueous
solution containing a hexavalent chromium compound, a
fluorine-containing compound and sulfuric acid, the method
comprising: the step of subjecting a steel sheet to treatment 1
including cathodic electrolysis treatment C1 using the aqueous
solution; and the step of subjecting the steel sheet having
undergone the cathodic electrolysis treatment C1 to treatment 2
including anodic electrolysis treatment A1 and cathodic
electrolysis treatment C2 following the anodic electrolysis
treatment A1, using the aqueous solution, at least two times.
6. The tin mill black plate manufacturing method according to claim
5, wherein a current density of the anodic electrolysis treatment
A1 is not less than 0.1 A/dm.sup.2 but less than 5.0 A/dm.sup.2,
wherein an electric quantity density of the anodic electrolysis
treatment A1 is more than 0.3 C/dm.sup.2 but less than 5.0
C/dm.sup.2, wherein a current density of the cathodic electrolysis
treatment C2 is less than 60.0 A/dm.sup.2, and wherein an electric
quantity density of the cathodic electrolysis treatment C2 is less
than 30.0 C/dm.sup.2.
7. The tin mill black plate manufacturing method according to claim
5, wherein the aqueous solution used in the cathodic electrolysis
treatment C1, the anodic electrolysis treatment A1 and the cathodic
electrolysis treatment C2 comprises only one type of aqueous
solution.
8. The tin mill black plate manufacturing method according to claim
6, wherein the aqueous solution used in the cathodic electrolysis
treatment C1, the anodic electrolysis treatment A1 and the cathodic
electrolysis treatment C2 comprises only one type of aqueous
solution.
Description
TECHNICAL FIELD
The present invention relates to a tin mill black plate and a
method of manufacturing the same.
BACKGROUND ART
Cans, which serve as containers for beverages and foods, are useful
for storing the contents over a long period of time and are
therefore used all over the world. Cans are roughly classified into
the following two types: a two-piece can that is obtained by
subjecting a metal sheet to drawing, ironing, stretching and
bending to integrally form a can bottom and a can body and then
joining the can body with a top lid by seaming; and a three-piece
can that is obtained by machining a metal sheet into a tubular
shape, welding the tubular metal sheet by a wire seam process to
form a can body, and then joining the opposite ends of the can body
separately with lids by seaming.
Conventionally, a tin-plated steel sheet (so-called tin plate) has
been widely used as a tin mill black plate.
Nowadays, an electrolytic chromate treated steel sheet (hereinafter
also called tin free steel (TFS)) having a chromium metal layer and
a hydrated chromium oxide layer is expanding its range of
application because it costs much less and is more excellent in
paint adhesion than tin plates.
In connection with reduction in washing waste liquid and CO.sub.2
for environmental reasons, cans using a steel sheet laminated with
an organic resin film such as PET (polyethylene terephthalate) is
drawing attention as an alternative technique that enables a
coating process and a subsequent baking process to be omitted. Also
in this context, the use of TFS having excellent adhesion to an
organic resin film is expected to continuously expand.
However, TFS is sometimes inferior in weldability to a tin plate.
This is because, due to bake hardening treatment after painting or
heat treatment after lamination of an organic resin film, a
hydrated chromium oxide layer in the surface layer initiates a
dehydration condensation reaction, and this leads to increased
contact resistance. In particular, bake hardening treatment after
painting requires a higher temperature than heat treatment after
lamination of an organic resin film, and therefore tends to result
in poorer weldability.
Accordingly, for TFS at present, a hydrated chromium oxide layer is
mechanically polished and removed immediately before welding to
thereby make welding possible.
In industrial production, however, there are many problems in that,
for instance, metal powder generated through polishing may be mixed
in the contents, a burden of maintenance such as cleaning of can
manufacturing equipment increases, and the risk of a fire caused by
metal powder increases.
To cope with it, a technique for welding TFS without polishing is
proposed by, for instance, Patent Literatures 1 and 2.
CITATION LIST
Patent Literatures
Patent Literature 1: JP 03-177599 A
Patent Literature 2: JP 04-187797 A
SUMMARY OF INVENTION
Technical Problems
In the technique disclosed by Patent Literatures 1 and 2, anodic
electrolysis treatment is carried out between prior-stage and
posterior-stage cathodic electrolysis treatments to thereby form a
large number of defect portions in a chromium metal layer, and then
chromium metal is formed into a shape of granular protrusions
through the posterior-stage cathodic electrolysis treatment.
According to this technique, it is expected that in welding, the
granular protrusions of chromium metal destroy a hydrated chromium
oxide layer that is a factor hindering welding in the surface
layer, thereby reducing contact resistance and improving
weldability.
However, the present inventors studied tin mill black plates
specifically described in Patent Literatures 1 and 2 and found
that, in some cases, they had insufficient weldability.
An object of the present invention is therefore to provide a tin
mill black plate having excellent weldability and a method of
manufacturing the same.
Solution to Problems
The present inventors have made an intensive study to achieve the
above-described object and as a result found that higher density of
granular protrusions in a chromium metal layer improves weldability
of a tin mill black plate. The present invention has been thus
completed.
Specifically, the present invention provides the following [1] to
[6].
[1] A tin mill black plate comprising, on a surface of a steel
sheet, a chromium metal layer and a hydrated chromium oxide layer
stacked in this order from a steel sheet side, wherein the chromium
metal layer has a coating weight of 50 to 200 mg/m.sup.2, wherein
the hydrated chromium oxide layer has a coating weight of 3 to 30
mg/m.sup.2 in terms of chromium amount, and wherein the chromium
metal layer includes a base portion with a thickness of not less
than 7.0 nm and granular protrusions provided on the base portion
and having a maximum diameter of not more than 200 nm and a number
density per unit area of not less than 30
protrusions/.mu.m.sup.2.
[2] The tin mill black plate according to [1] above, wherein the
hydrated chromium oxide layer has a coating weight of more than 15
mg/m.sup.2 but not more than 30 mg/m.sup.2 in terms of chromium
amount.
[3] The tin mill black plate according to [1] or [2] above, wherein
the granular protrusions have a number density per unit area of not
less than 200 protrusions/pmt.
[4] A tin mill black plate manufacturing method for obtaining the
tin mill black plate according to any one of [1] to [3] above by
use of an aqueous solution containing a hexavalent chromium
compound, a fluorine-containing compound and sulfuric acid, the
method comprising: the step of subjecting a steel sheet to
treatment 1 including cathodic electrolysis treatment C1 using the
aqueous solution; and the step of subjecting the steel sheet having
undergone the cathodic electrolysis treatment C1 to treatment 2
including anodic electrolysis treatment A1 and cathodic
electrolysis treatment C2 following the anodic electrolysis
treatment A1, using the aqueous solution, at least two times.
[5] The tin mill black plate manufacturing method according to [4]
above, wherein a current density of the anodic electrolysis
treatment A1 is not less than 0.1 A/dm.sup.2 but less than 5.0
A/dm.sup.2, wherein an electric quantity density of the anodic
electrolysis treatment A1 is more than 0.3 C/dm.sup.2 but less than
5.0 C/dm.sup.2, wherein a current density of the cathodic
electrolysis treatment C2 is less than 60.0 A/dm.sup.2, and wherein
an electric quantity density of the cathodic electrolysis treatment
C2 is less than 30.0 C/dm.sup.2.
[6] The tin mill black plate manufacturing method according to [4]
or [5] above, wherein the aqueous solution used in the cathodic
electrolysis treatment C1, the anodic electrolysis treatment A1 and
the cathodic electrolysis treatment C2 comprises only one type of
aqueous solution.
Advantageous Effects of Invention
The present invention provides a tin mill black plate having
excellent weldability and a method of manufacturing the same.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional view schematically showing one example
of a tin mill black plate of the invention.
DESCRIPTION OF EMBODIMENTS
[Tin Mill Black Plate]
FIG. 1 is a cross-sectional view schematically showing one example
of a tin mill black plate of the invention.
As shown in FIG. 1, a tin mill black plate 1 includes a steel sheet
2. The tin mill black plate 1 further includes, on a surface of the
steel sheet 2, a chromium metal layer 3 and a hydrated chromium
oxide layer 4 stacked in this order from the steel sheet 2
side.
The chromium metal layer 3 includes a base portion 3a covering the
steel sheet 2 and granular protrusions 3b provided on the base
portion 3a. The base portion 3a has a thickness of at least 7.0 nm.
The granular protrusions 3b have a maximum diameter of not more
than 200 nm and a number density per unit area of not less than 30
protrusions/.mu.m.sup.2. The chromium metal layer 3 including the
base portion 3a and the granular protrusions 3b has a coating
weight of 50 to 200 mg/m.sup.2.
The hydrated chromium oxide layer 4 is disposed on the chromium
metal layer 3 to conform the shape of the granular protrusions 3b.
The hydrated chromium oxide layer 4 has a coating weight of 3 to 30
mg/m.sup.2 in terms of chromium amount.
The coating weight refers to the coating weight per one side of the
steel sheet.
The constituent elements of the invention are described in detail
below.
<Steel Sheet>
The type of the steel sheet is not particularly limited. In
general, steel sheets used as materials for containers (e.g., a low
carbon steel sheet and an ultra low carbon steel sheet) can be
used. A manufacturing method of the steel sheet, a material thereof
and the like are also not particularly limited. The steel sheet is
manufactured through a process starting with a typical billet
manufacturing process, followed by such processes as hot rolling,
pickling, cold rolling, annealing and temper rolling.
<Chromium Metal Layer>
The tin mill black plate of the invention has a chromium metal
layer on a surface of the foregoing steel sheet.
The role of chromium metal in typical TFS is to reduce the exposure
of a surface of the steel sheet serving as the base material and
thereby improve corrosion resistance. When the amount of chromium
metal is too small, the steel sheet is inevitably exposed, and this
may lead to poor corrosion resistance.
The coating weight of the chromium metal layer is not less than 50
mg/m.sup.2 because this leads to excellent corrosion resistance of
the tin mill black plate, and is preferably not less than 60
mg/m.sup.2, more preferably not less than 65 mg/m.sup.2 and still
more preferably not less than 70 mg/m.sup.2 because this leads to
further excellent corrosion resistance.
In contrast, when the amount of chromium metal is too large,
high-melting chromium metal is to cover the entire surface of the
steel sheet, and this induces significant decrease in weld strength
in welding and significant generation of dust, which may lead to
poor weldability.
The coating weight of the chromium metal layer is not more than 200
mg/m.sup.2 because this leads to excellent weldability of the tin
mill black plate, and is preferably not more than 180 mg/m.sup.2
and more preferably not more than 160 mg/m.sup.2 because this leads
to further excellent weldability.
Measurement Methods of Coating Weights
The coating weight of the chromium metal layer and the coating
weight of the hydrated chromium oxide layer (described later) in
terms of chromium amount are measured as follows.
First, for the tin mill black plate having formed thereon the
chromium metal layer and the hydrated chromium oxide layer, the
amount of chromium (total amount of chromium) is measured with an
X-ray fluorescence device. Next, the tin mill black plate is
subjected to alkaline treatment, i.e., is immersed in 6.5N-NaOH at
90.degree. C. for 10 minutes, and then, again, the amount of
chromium (amount of chromium after alkaline treatment) is measured
with an X-ray fluorescence device. The amount of chromium after
alkaline treatment is taken as the coating weight of the chromium
metal layer.
Thereafter, the equation (amount of alkali-soluble chromium)=(total
amount of chromium)-(amount of chromium after alkaline treatment)
is calculated, and the amount of alkali-soluble chromium is taken
as the coating weight of the hydrated chromium oxide layer in terms
of chromium amount.
The chromium metal layer as above includes a base portion and
granular protrusions provided on the base portion.
Next, those portions included in the chromium metal layer are
described in detail.
Base Portion of Chromium Metal Layer
The base portion of the chromium metal layer mainly serves to
improve corrosion resistance by covering a surface of the steel
sheet.
The base portion of the chromium metal layer in the invention needs
to have, in addition to corrosion resistance which is generally
required of TFS, a uniform and sufficient thickness such that the
base portion is not destroyed by the granular protrusions provided
in the surface layer, thus preventing the exposure of the steel
sheet, when the tin mill black plate inevitably comes into contact
with another tin mill black plate at handling.
In connection with this, the present inventors conducted a rubbing
test of a tin mill black plate with another tin mill black plate so
as to check rust resistance and as a result found that, when the
base portion of the chromium metal layer has a thickness of not
less than 7.0 nm, the rust resistance is excellent. More
specifically, the thickness of the base portion of the chromium
metal layer is not less than 7.0 nm because this leads to excellent
rust resistance of the tin mill black plate, and is preferably not
less than 9.0 nm and more preferably not less than 10.0 nm because
this leads to further excellent rust resistance.
The upper limit of the thickness of the base portion of the
chromium metal layer is not particularly limited and is, for
instance, not more than 20.0 nm and preferably not more than 15.0
nm.
(Measurement Method of Thickness)
The thickness of the base portion of the chromium metal layer is
measured as follows.
First, a cross section sample of a tin mill black plate having
formed thereon a chromium metal layer and a hydrated chromium oxide
layer is produced by a focused ion beam (FIB) method and observed
at a magnification of 20,000.times. with a scanning transmission
electron microscope (TEM). Next, in a sectional shape observation
on a bright-field image, focusing on a portion where only a base
portion is present with no granular protrusions, a line analysis is
conducted by energy dispersive X-ray spectrometry (EDX) to obtain
intensity curves (horizontal axis: distance, vertical axis:
intensity) of chromium and iron, and those curves are used to
determine the thickness of the base portion. To be more specific,
in the chromium intensity curve, the point at which the intensity
is 20% of the maximum is taken as the uppermost layer, while the
cross point with the iron intensity curve is taken as the boundary
point with iron, and the distance between those two points is taken
as the thickness of the base portion.
The coating weight of the base portion of the chromium metal layer
is preferably not less than 10 mg/m.sup.2, more preferably not less
than 30 mg/m.sup.2 and even more preferably not less than 40
mg/m.sup.2 because this leads to excellent rust resistance of the
tin mill black plate.
Granular Protrusions of Chromium Metal Layer
The granular protrusions of the chromium metal layer are formed on
a surface of the base portion described above, and mainly serve to
improve weldability by reducing contact resistance between
to-be-welded portions of the tin mill black plate. The assumed
mechanism of reduction in contact resistance is described
below.
The hydrated chromium oxide layer covering the chromium metal layer
is a non-conductive coating and therefore has higher electric
resistance than chromium metal, so that the hydrated chromium oxide
layer works as a factor hindering welding. By forming the granular
protrusions on a surface of the base portion of the chromium metal
layer, the granular protrusions act to destroy the hydrated
chromium oxide layer using the surface pressure applied when
to-be-welded portions of the tin mill black plate come into contact
with each other in welding, and the granular protrusions become
current-carrying points of welding current, whereby the contact
resistance greatly decreases.
When the number of the granular protrusions of the chromium metal
layer is too small, current-carrying points in welding decrease in
number, and this may prevent the contact resistance from being
lowered, resulting in poor weldability. When the granular
protrusions are formed to be present at high density, the contact
resistance is lowered even if the hydrated chromium oxide layer,
which is an insulating layer, is thick. Thus, the paint adhesion,
the under film corrosion resistance, the weldability and other
properties can be achieved in good balance.
The number density of the granular protrusions per unit area is not
less than 30 protrusions/.mu.m.sup.2 because this leads to
excellent weldability of the tin mill black plate, and is
preferably not less than 200 protrusions/.mu.m.sup.2, more
preferably not less than 1,000 protrusions/.mu.m.sup.2 and even
more preferably more than 1,000 protrusions/.mu.m.sup.2 because
this leads to further excellent weldability.
Because too high a number density of the granular protrusions per
unit area may affect the color tone or the like, the upper limit of
the number density per unit area is preferably not more than 10,000
protrusions/.mu.m.sup.2 and more preferably not more than 5,000
protrusions/.mu.m.sup.2 for the reason that this allows the tin
mill black plate to have a further excellent surface
appearance.
Meanwhile, the present inventors found that, when the maximum
diameter of the granular protrusions of the chromium metal layer is
too large, this affects the color tone or the like of the tin mill
black plate, and a brown pattern appears in some cases, resulting
in a poor surface appearance. The possible reasons of the above are
for example as follows: the granular protrusions absorb
short-wavelength (blue) light, and accordingly, reflected light
thereof is attenuated, so that a reddish brown color appears; the
granular protrusions diffuse reflected light, so that the overall
reflectance decreases and the color gets darker.
Therefore, the maximum diameter of the granular protrusions of the
chromium metal layer is set to 200 nm or less. As a result, the tin
mill black plate can have an excellent surface appearance. This is
probably because the granular protrusions with a smaller diameter
serve to suppress absorption of short-wavelength light and suppress
dispersion of reflected light.
The maximum diameter of the granular protrusions of the chromium
metal layer is preferably not more than 150 nm, more preferably not
more than 100 nm and even more preferably not more than 80 nm
because this leads to a further excellent surface appearance of the
tin mill black plate.
The lower limit of the maximum diameter is not particularly limited
and is preferably, for instance, not less than 10 nm.
(Measurement Methods of Diameter of Granular Protrusions and Number
Density Thereof per Unit Area)
The diameter of the granular protrusions of the chromium metal
layer and the number density thereof per unit area are measured as
follows.
First, a surface of the tin mill black plate having formed thereon
the chromium metal layer and the hydrated chromium oxide layer is
subjected to carbon deposition to produce an observation sample by
an extraction replica method. Subsequently, a micrograph of the
sample is taken at a magnification of 20,000.times. with a scanning
transmission electron microscope (TEM), the taken micrograph is
binarized using software (trade name: ImageJ) and subjected to
image analysis, and the diameter (as a true circle-equivalent
value) and the number density per unit area are determined through
back calculation from the area occupied by the granular
protrusions. The maximum diameter is the diameter that is maximum
in observation fields as obtained by taking micrographs of five
fields at a magnification of 20,000.times., and the number density
per unit area is the average of number densities of the five
fields.
<Hydrated Chromium Oxide Layer>
A hydrated chromium oxide is deposited along with chromium metal on
a surface of the steel sheet and mainly serves to improve corrosion
resistance. A hydrated chromium oxide also serves to improve both
corrosion resistance after painting, such as under film corrosion
resistance, and paint adhesion. The coating weight of the hydrated
chromium oxide layer in terms of chromium amount is not less than 3
mg/m.sup.2 in order to ensure corrosion resistance and paint
adhesion of the tin mill black plate, and is preferably not less
than 10 mg/m.sup.2 and more preferably more than 15 mg/m.sup.2
because this leads to further excellent corrosion resistance and
paint adhesion.
Meanwhile, a hydrated chromium oxide is inferior to chromium metal
in conductivity, and accordingly, too much amount of hydrated
chromium oxide leads to excessive resistance in welding, which may
cause generation of dust, occurrence of splash, and a variety of
weld defects such as blowhole formation associated with
overwelding, thus resulting in poor weldability of the tin mill
black plate.
Therefore, the coating weight of the hydrated chromium oxide layer
in terms of chromium amount is not more than 30 mg/m.sup.2 because
this leads to excellent weldability of the tin mill black plate,
and is preferably not more than 25 mg/m.sup.2 and more preferably
not more than 20 mg/m.sup.2 because this leads to further excellent
weldability.
The measurement method of the coating weight of the hydrated
chromium oxide layer in terms of chromium amount is as described
above.
[Tin Mill Black Plate Manufacturing Method]
Next, the tin mill black plate manufacturing method according to
the present invention is described.
The tin mill black plate manufacturing method according to the
present invention (hereinafter also simply called "manufacturing
method of the invention") is a method of manufacturing the
foregoing tin mill black plate of the invention by use of an
aqueous solution containing a hexavalent chromium compound, a
fluorine-containing compound and sulfuric acid, the method
comprising: the step of subjecting a steel sheet to treatment 1
including cathodic electrolysis treatment C1 using the aqueous
solution; and the step of subjecting the steel sheet having
undergone the cathodic electrolysis treatment C1 to treatment 2
including anodic electrolysis treatment A1 and cathodic
electrolysis treatment C2 following the anodic electrolysis
treatment A1, using the aqueous solution, at least two times.
Typically, in cathodic electrolysis treatment in an aqueous
solution containing a hexavalent chromium compound, a reduction
reaction occurs at a steel sheet surface, whereby chromium metal is
deposited, and a hydrated chromium oxide that is an intermediate
product before becoming chromium metal is deposited on the chromium
metal surface. This hydrated chromium oxide is unevenly dissolved
through intermittent electrolysis treatment or long time immersion
in an aqueous solution of a hexavalent chromium compound, and in
the subsequent cathodic electrolysis treatment, granular
protrusions of chromium metal are formed.
Since the anodic electrolysis treatment is carried out between the
two cathodic electrolysis treatments, chromium metal is dissolved
over the entire surface of the steel sheet at multiple sites, and
those sites become starting points of formation of the granular
protrusions of chromium metal in the subsequent cathodic
electrolysis treatment. The base portion of the chromium metal
layer is deposited in the cathodic electrolysis treatment C1 before
the anodic electrolysis treatment A1, and the granular protrusions
of the chromium metal layer are deposited in the cathodic
electrolysis treatment C2 after the anodic electrolysis treatment
A1.
The amounts of deposition of those portions can be controlled by
electrolysis conditions in the respective electrolysis
treatments.
The aqueous solution and the electrolysis treatments used in the
manufacturing method of the invention are described in detail
below.
<Aqueous Solution>
The aqueous solution used in the manufacturing method of the
invention contains a hexavalent chromium compound, a
fluorine-containing compound and sulfuric acid.
A fluorine-containing compound and sulfuric acid in the aqueous
solution are dissociated and are present as fluoride ions, sulfate
ions and hydrogen sulfate ions. These substances serve as catalysts
involved in those reduction reaction and oxidation reaction of
hexavalent chromium ions in the aqueous solution which proceed in
the cathodic and anodic electrolysis treatments, and the substances
are therefore typically added as auxiliary agents in a chromium
plating bath.
When the aqueous solution used in the electrolysis treatments
contains a fluorine-containing compound and sulfuric acid, this can
reduce the coating weight of the hydrated chromium oxide layer of
the resulting tin mill black plate in terms of chromium amount. The
mechanism of this reduction is not clear but it is assumed that the
increase in the amount of anions in electrolysis treatment brings
about the decrease in the amount of generated oxides.
It is preferable that one type of aqueous solution be solely used
in the cathodic electrolysis treatment C1, the anodic electrolysis
treatment A1 and the cathodic electrolysis treatment C2.
Hexavalent Chromium Compound
The hexavalent chromium compound contained in the aqueous solution
is not particularly limited, and examples thereof include chromium
trioxide (CrO.sub.3), dichromates such as potassium dichromate
(K.sub.2Cr.sub.2O.sub.7), and chromates such as potassium chromate
(K.sub.2CrO.sub.4).
The hexavalent chromium compound content of the aqueous solution is
preferably from 0.14 to 3.00 mol/L and more preferably from 0.30 to
2.50 mol/L in the amount of Cr.
Fluorine-containing Compound
The fluorine-containing compound contained in the aqueous solution
is not particularly limited, and examples thereof include
hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride
(NaF), hydrosilicofluoric acid (H.sub.2SiF.sub.6) and/or salts
thereof. Examples of salts of hydrosilicofluoric acid include
sodium silicofluoride (Na.sub.2SiF.sub.6), potassium silicofluoride
(K.sub.2SiF.sub.6), and ammonium silicofluoride
((NH.sub.4).sub.2SiF.sub.6).
The fluorine-containing compound content of the aqueous solution is
preferably from 0.02 to 0.48 mol/L and more preferably from 0.08 to
0.40 mol/L in the amount of F.
Sulfuric Acid
The sulfuric acid (H.sub.2SO.sub.4) content of the aqueous solution
is preferably from 0.0001 to 0.1000 mol/L, more preferably 0.0003
to 0.0500 mol/L and even more preferably 0.0010 to 0.0500 mol/L in
the amount of SO.sub.4.sup.2-.
The use of the sulfuric acid in combination with the
fluorine-containing compound improves electrolysis efficiency in
deposition of the chromium metal layer. When the sulfuric acid
content of the aqueous solution falls within the foregoing ranges,
the size of the granular protrusions of the chromium metal layer to
be deposited in the cathodic electrolysis treatment C2 can be
easily controlled to an appropriate range.
In addition, the sulfuric acid also influences the formation of
generation sites where the granular protrusions of the chromium
metal layer are generated in the anodic electrolysis treatment.
When the sulfuric acid content of the aqueous solution falls within
the foregoing ranges, this prevents the granular protrusions of the
chromium metal layer from being excessively fine or coarse, and the
proper number density can be achieved more easily.
The temperature of the aqueous solution in each electrolysis
treatment is preferably 20.degree. C. to 80.degree. C. and more
preferably 40.degree. C. to 60.degree. C.
<Cathodic Electrolysis Treatment C1 (Treatment 1)>
The cathodic electrolysis treatment C1 is carried out to deposit
chromium metal and a hydrated chromium oxide.
The electric quantity density (the product of the current density
and the current application time) in the cathodic electrolysis
treatment C1 is preferably 20 to 50 C/dm.sup.2 and more preferably
25 to 45 C/dm.sup.2 for the purpose of achieving a proper amount of
deposition and ensuring an appropriate thickness of the base
portion of the chromium metal layer.
The current density (unit: A/dm.sup.2) and the current application
time (unit: sec.) are suitably set based on the foregoing electric
quantity density.
The cathodic electrolysis treatment C1 need not be continuous
electrolysis treatment. In other words, the cathodic electrolysis
treatment C1 may be intermittent electrolysis treatment because
electrolysis is carried out separately for each set of electrodes
in industrial production and accordingly, an immersion period with
no current application is inevitably present. In the case of
intermittent electrolysis treatment, the total electric quantity
density preferably falls within the foregoing ranges.
<Anodic Electrolysis Treatment A1>
The anodic electrolysis treatment A1 serves to dissolve chromium
metal deposited in the cathodic electrolysis treatment C1 so as to
form the generation sites of the granular protrusions of the
chromium metal layer to be generated in the cathodic electrolysis
treatment C2.
When dissolution excessively proceeds in the anodic electrolysis
treatment A1, this may cause a decreased number of generation sites
and hence a lower number density of the granular protrusions per
unit area, variation in distribution of the granular protrusions
due to uneven progress of dissolution, and a small thickness of the
base portion of the chromium metal layer of less than 7.0 nm.
Besides, when the current density of the anodic electrolysis
treatment A1 is too high, this may adversely affect corrosion
resistance and other properties. This is probably because part of
the chromium metal layer is dissolved more than necessary, and
accordingly, the generation sites with the base portion of the
chromium metal layer having a thickness of less than 7.0 nm are
locally formed.
The chromium metal layer formed through the cathodic electrolysis
treatment C1 and the first anodic electrolysis treatment A1 is
mainly the base portion. In order to have the base portion of the
chromium metal layer with a thickness of 7.0 nm or more, it is
necessary to ensure the chromium metal amount of not less than 50
mg/m.sup.2 after the cathodic electrolysis treatment C1 and the
first anodic electrolysis treatment A1.
Thus, in order to facilitate formation of the chromium metal layer
having the granular protrusions in the subsequent cathodic
electrolysis treatment C2, the current density of the anodic
electrolysis treatment A1 (i.e., the current density of each of the
anodic electrolysis treatments A1 that are carried out at least two
times) is suitably adjusted, and is preferably not less than 0.1
A/dm.sup.2 but less than 5.0 A/dm.sup.2.
A current density of not lower than 0.1 A/dm.sup.2 is favorable
because this leads to formation of a sufficient number of
generation sites of the granular protrusions, which makes it easy
to sufficiently generate and uniformly distribute the granular
protrusions in the subsequent cathodic electrolysis treatment
C2.
A current density of less than 5.0 A/dm.sup.2 is favorable because
this leads to excellent rust resistance and under film corrosion
resistance. This is probably because chromium metal is prevented
from dissolving in an unnecessarily excessive amount in a single
anodic electrolysis treatment, so that the generation sites of the
granular protrusions do not excessively grow, thus preventing the
base portion of the chromium metal layer from locally becoming
thin.
The electric quantity density of the anodic electrolysis treatment
A1 (i.e., the electric quantity density of each of the anodic
electrolysis treatments A1 that are carried out at least two times)
is preferably more than 0.3 C/dm.sup.2 but less than 5.0
C/dm.sup.2, more preferably more than 0.3 C/dm.sup.2 but not more
than 3.0 C/dm.sup.2, and even more preferably more than 0.3
C/dm.sup.2 but not more than 2.0 C/dm.sup.2. The electric quantity
density is a product of the current density and the current
application time.
The current application time (unit: sec.) is suitably set based on
the foregoing current density (unit: A/dm.sup.2) and electric
quantity density (unit: C/dm.sup.2).
The anodic electrolysis treatment A1 need not be continuous
electrolysis treatment. In other words, the anodic electrolysis
treatment A1 may be intermittent electrolysis treatment because
electrolysis is carried out separately for each set of electrodes
in industrial production and accordingly, an immersion period with
no current application is inevitably present. In the case of
intermittent electrolysis treatment, the total electric quantity
density preferably falls within the foregoing ranges.
<Cathodic Electrolysis Treatment C2>
As described above, cathodic electrolysis treatment is carried out
to deposit chromium metal and a hydrated chromium oxide. In
particular, the cathodic electrolysis treatment C2 allows the
granular protrusions of the chromium metal layer to be generated at
the foregoing generation sites serving as starting points. In this
process, when the current density and the electric quantity density
are too high, the granular protrusions of the chromium metal layer
may excessively grow, leading to a coarse grain size.
For this reason, the current density of the cathodic electrolysis
treatment C2 (i.e., the current density of each of the cathodic
electrolysis treatments C2 that are carried out at least two times)
is preferably less than 60.0 A/dm.sup.2, more preferably less than
50.0 A/dm.sup.2 and even more preferably less than 40.0 A/dm.sup.2.
The lower limit thereof is not particularly limited and is
preferably not less than 10.0 A/dm.sup.2 and more preferably more
than 15.0 A/dm.sup.2.
For the same reason, the electric quantity density of the cathodic
electrolysis treatment C2 (i.e., the electric quantity density of
each of the cathodic electrolysis treatments C2 that are carried
out at least two times) is preferably less than 30.0 C/dm.sup.2,
more preferably not more than 25.0 C/dm.sup.2 and even more
preferably not more than 7.0 C/dm.sup.2. The lower limit thereof is
not particularly limited and is preferably not less than 1.0
C/dm.sup.2 and more preferably not less than 2.0 C/dm.sup.2.
The current application time (unit: sec.) is suitably set based on
the foregoing current density and electric quantity density.
The cathodic electrolysis treatment C2 need not be continuous
electrolysis treatment. In other words, the cathodic electrolysis
treatment C2 may be intermittent electrolysis treatment because
electrolysis is carried out separately for each set of electrodes
in industrial production and accordingly, an immersion period with
no current application is inevitably present. In the case of
intermittent electrolysis treatment, the total electric quantity
density preferably falls within the foregoing ranges.
<Number of Times of Treatment 2 including A1 and C2>
In the manufacturing method of the invention, the steel sheet
having undergone the cathodic electrolysis treatment C1 is
subjected to the treatment 2 including the anodic electrolysis
treatment A1 and the cathodic electrolysis treatment C2 at least
two times.
The number of times of the treatment 2 is preferably at least
three, more preferably at least five and even more preferably at
least seven. When the treatment 2 as above is repeated, this means
that the formation of the generation sites of the granular
protrusions of the chromium metal layer (anodic electrolysis
treatment A1) and the formation of the granular protrusions of the
chromium metal layer (cathodic electrolysis treatment C2) are
repeated; therefore, the granular protrusions of the chromium metal
layer can be uniformly formed at high density. Owing to this
configuration, even when the coating weight of the hydrated
chromium oxide layer is increased to improve corrosion resistance
and other properties, the granular protrusions that are uniformly
present at high density act to increase the number of contact
points in welding, thus reducing contact resistance and achieving
excellent weldability.
The upper limit of the number of times of the treatment 2 as above
is not particularly limited; however, for the purpose of
controlling the thickness of the base portion of the chromium metal
layer formed in the cathodic electrolysis treatment C1 to a proper
range, the treatment 2 is preferably not excessively repeated and
is, for instance, repeated up to 30 times and preferably up to 20
times.
<Post-Treatment>
The treatment 2 including the anodic electrolysis treatment A1 and
the cathodic electrolysis treatment C2 may be followed by
post-treatment.
For example, in order to ensure paint adhesion and under film
corrosion resistance, the steel sheet may be subjected to immersion
treatment or cathodic electrolysis treatment using an aqueous
solution containing a hexavalent chromium compound for the purposes
of controlling the amount of hydrated chromium oxide layer,
modifying that layer, and other purposes.
Even when the post-treatment as above is carried out, the thickness
of the base portion of the chromium metal layer and the diameter
and the number density of the granular protrusions are not affected
thereby.
The hexavalent chromium compound contained in the aqueous solution
used in the post-treatment is not particularly limited, and
examples thereof include chromium trioxide (CrO.sub.3), dichromates
such as potassium dichromate (K.sub.2Cr.sub.2O.sub.7), and
chromates such as potassium chromate (K.sub.2CrO.sub.4).
EXAMPLES
The present invention is specifically described below with
reference to examples. However, the present invention should not be
construed as being limited to the following examples.
<Manufacture of Tin Mill Black Plate>
Each steel sheet (tempered grade: T4CA) as produced to a sheet
thickness of 0.22 mm was subjected to normal degreasing and
pickling. Subsequently, the relevant aqueous solution shown in
Table 1 below was circulated by a pump at a rate equivalent to 100
mpm in a fluid cell, and electrolysis treatment was carried out
using lead electrodes under the conditions shown in Table 2 below,
thereby manufacturing a tin mill black plate that is TFS. The tin
mill black plate as manufactured was rinsed with water and dried by
a blower at room temperature.
To be more specific, first, the treatment 1 including the cathodic
electrolysis treatment C1, and the treatment 2 including the anodic
electrolysis treatment A1 and the cathodic electrolysis treatment
C2 were carried out in this order by use of one of aqueous
solutions A to D. The number of times of the treatment 2 was two or
more, while the treatment 2 was carried out only once in some
comparative examples. In some examples, the treatment 2 was
followed by the post-treatment (cathodic electrolysis treatment or
immersion treatment) using an aqueous solution E.
As to the cases that the treatment 2 including the anodic
electrolysis treatment A1 and the cathodic electrolysis treatment
C2 was carried out two or more times, the current density and the
electric quantity density shown in Table 2 below were the values of
each time.
For instance, in Example 1 (number of times of treatment 2: 2)
shown in Table 2 below, the first cathodic electrolysis treatment
C2 was carried out with a current density of 30.0 A/dm.sup.2 and an
electric quantity density of 15.0 C/dm.sup.2, and the second
cathodic electrolysis treatment C2 was carried out with a current
density of 30.0 A/dm.sup.2 and an electric quantity density of 15.0
C/dm.sup.2.
<Coating Weight>
For each of the manufactured tin mill black plates, the coating
weight of the chromium metal layer (Cr metal layer) and the coating
weight of the hydrated chromium oxide layer (hydrated Cr oxide
layer) in terms of chromium amount (stated simply as "Coating
weight" in Table 3 below) were measured. The measurement methods
are as described above. The results are shown in Table 3 below.
<Cr Metal Layer Structure>
For the Cr metal layer of each of the manufactured tin mill black
plates, the thickness of the base portion and the maximum diameter
and the number density per unit area of the granular protrusions
were measured. The measurement methods are as described above. The
results are shown in Table 3 below.
<Evaluation>
The manufactured tin mill black plates were evaluated for the
following factors. The evaluation results are shown in Table 3
below.
Rust Resistance 1: Rust Resistance Test of Abraded Steel Sheet
A rust resistance test of an abraded steel sheet is conducted to
evaluate rust resistance. Specifically, two samples were cut out
from each of the manufactured tin mill black plates. One sample (30
mm.times.60 mm) was fixed to a rubbing tester for use as an
evaluation sample, while the other sample (10 mm.times.10 mm) was
fixed to a head, and the head was moved 10 strokes over a length of
60 mm at a surface pressure of 1 kgf/cm.sup.2 and a rubbing rate of
1 second per reciprocation. Thereafter, the evaluation sample was
allowed to stand in a constant temperature and humidity chamber at
40.degree. C. and 80% RH for 7 days. Then, the evaluation sample
was observed at low magnification with an optical microscope, and a
micrograph thereof was subjected to image analysis to determine the
rusting area fraction of a rubbed portion. The evaluation was made
according to the following criteria. For practical use, when the
result is A, B or C, the tin mill black plate can be rated as
having excellent rust resistance.
A: A rusting area fraction of less than 1%
B: A rusting area fraction of not less than 1% but less than 2%
C: A rusting area fraction of not less than 2% but less than 5%
D: A rusting area fraction of not less than 5% but less than
10%
E: A rusting area fraction of not less than 10%, or rusting at
somewhere other than a rubbed portion.
Rust Resistance 2: Storage Rust Test Twenty samples of 100
mm.times.100 mm were cut out from each of the manufactured tin mill
black plates, stacked, wrapped with anti-rust paper, sandwiched by
pieces of plywood to be thereby fixed, and then allowed to stand in
a constant temperature and humidity chamber at 30.degree. C. and
85% RH for 2 months. Thereafter, the area fraction of rust that
occurred on superposed surfaces (rust area fraction) was observed
and evaluated according to the following criteria. For practical
use, when the result is A, B or C, the tin mill black plate can be
rated as having excellent rust resistance.
A: No rusting
B: A very little rusting or a rust area fraction of less than
0.1%
C: A rust area fraction of not less than 0.1% but less than
0.3%
D: A rust area fraction of not less than 0.3% but less than
0.5%
E: A rust area fraction of not less than 0.5%
Surface Appearance (Color Tone)
For each of the manufactured tin mill black plates, the L value was
measured according to the Hunter-type color difference measurement
defined in JIS Z 8730 of old version (1980) and evaluated according
to the following criteria. For practical use, when the result is A,
B or C, the tin mill black plate can be rated as having an
excellent surface appearance.
A: An L value of not less than 65
B: An L value of not less than 60 but less than 65
C: An L value of not less than 55 but less than 60
D: An L value of not less than 50 but less than 55
E: An L value of less than 50
Weldability (Contact Resistance)
Each of the manufactured tin mill black plates was subjected to
heat treatment of 210.degree. C..times.10 minutes two times, and
then the contact resistance was measured. More specifically,
samples of each tin mill black plate were heated (and retained at a
target plate temperature of 210.degree. C. for 10 minutes) in a
batch furnace, and the samples having undergone the heat treatment
were superposed. Subsequently, 1 mass Cr-Cu electrodes of DR type
were machined to a tip diameter of 6 mm and a curvature of R40 mm,
the superposed samples were sandwiched by these electrodes and
retained at a pressure of 1 kgf/cm.sup.2 for 15 seconds, then 10A
current was supplied thereto, and the contact resistance between
the sample plates was measured. The measurement was made for ten
cases, and the average thereof was taken as a contact resistance
value to be evaluated according to the following criteria. For
practical use, when the result is
AA, A, B or C, the tin mill black plate can be rated as having
excellent weldability.
AA: Contact resistance of not more than 20.mu..OMEGA.
A: Contact resistance of more than 20 .mu..OMEGA. but not more than
100.mu..OMEGA.
B: Contact resistance of more than 100 .mu..OMEGA. but not more
than 300.mu..OMEGA.
C: Contact resistance of more than 300 .mu..OMEGA. but not more
than 500.mu..OMEGA.
D: Contact resistance of more than 500 .mu..OMEGA. but not more
than 1000.mu..OMEGA.
E: Contact resistance of more than 1000.mu..OMEGA.
Primary Paint Adhesion
Each of the manufactured tin mill black plates was applied with
epoxy-phenolic resin and subjected to heat treatment of 210.degree.
C..times.10 minutes two times. Subsequently, cuts reaching the
steel sheet were made at intervals of 1 mm in a grid pattern.
Peeling was carried out using tape, and the peeling state was
observed. The peeling area fraction was evaluated according to the
following criteria. For practical use, when the result is A, B or
C, the tin mill black plate can be rated as having excellent
primary paint adhesion.
A: A peeling area fraction of 0%
B: A peeling area fraction of more than 0% but not more than 2%
C: A peeling area fraction of more than 2% but not more than 5%
D: A peeling area fraction of more than 5% but not more than
30%
E: A peeling area fraction of more than 30%
Secondary Paint Adhesion
Each of the manufactured tin mill black plates was applied with
epoxy-phenolic resin and subjected to heat treatment of 210.degree.
C..times.10 minutes two times. Subsequently, cuts reaching the
steel sheet were made at intervals of 1 mm in a grid pattern,
retort treatment was carried out at 125.degree. C. for 30 minutes.
After drying, peeling was carried out using tape, and the peeling
state was observed. The peeling area fraction was evaluated
according to the following criteria. For practical use, when the
result is A, B or C, the tin mill black plate can be rated as
having excellent secondary paint adhesion.
A: A peeling area fraction of 0%
B: A peeling area fraction of more than 0% but not more than 2%
C: A peeling area fraction of more than 2% but not more than 5%
D: A peeling area fraction of more than 5% but not more than
30%
E: A peeling area fraction of more than 30%
Under Film Corrosion Resistance
Each of the manufactured tin mill black plates was applied with
epoxy-phenolic resin and subjected to heat treatment of 210.degree.
C..times.10 minutes two times. A cross cut reaching the steel sheet
was made, and the resulting tin mill black plate was immersed in a
test solution that was a mixed aqueous solution of 1.5% citric acid
and 1.5% NaCl at 45.degree. C. for 72 hours. Immersion was followed
by rinsing and drying, and then tape peeling was carried out. The
peeled width (i.e., the total width of peeled portions extending to
right and left from a cut portion) was measured at four places
within 10 mm from the crossing point of the cross cut, and the
average of measurements at the four places was obtained. The
average of the peeled widths was defined as an under film corroded
width and evaluated according to the following criteria. For
practical use, when the result is A, B or C, the tin mill black
plate can be rated as having excellent under film corrosion
resistance.
A: A corroded width of not more than 0.2 mm
B: A corroded width of more than 0.2 mm but not more than 0.3
mm
C: A corroded width of more than 0.3 mm but not more than 0.4
mm
D: A corroded width of more than 0.4 mm but not more than 0.5
mm
E: A corroded width of more than 0.5 mm
TABLE-US-00001 TABLE 1 Aqueous solution Composition A CrO.sub.3
0.50 mol/L NaF 0.20 mol/L H.sub.2SO.sub.4 0.0100 mol/L B CrO.sub.3
0.75 mol/L NaF 0.20 mol/L H.sub.2SO.sub.4 0.0100 mol/L C CrO.sub.3
1.00 mol/L NaF 0.20 mol/L H.sub.2SO.sub.4 0.0100 mol/L D CrO.sub.3
0.50 mol/L NaF 0.10 mol/L H.sub.2SO.sub.4 0.0100 mol/L E CrO.sub.3
0.60 mol/L NH.sub.4F 0.048 mol/L
TABLE-US-00002 TABLE 2 Treatment 1 and Treatment 2 Treatment 1
Treatment 2 Cathodic electrolysis Anodic electrolysis treatment C1
treatment A1 Cathodic electrolysis Current Electric Current
Electric treatment C2 Current application quantity Current
application quantity Current Aqueous Temp. density time density
density time density density solution .degree. C. A/dm.sup.2 sec.
C/dm.sup.2 A/dm.sup.2 sec. C/dm.sup.2 A/dm.sup.2 EX 1 A 45 30.0
1.00 30.0 1.0 0.50 0.5 30.0 EX 2 A 45 30.0 1.00 30.0 1.0 0.50 0.5
30.0 EX 3 A 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 4 A 45 30.0 1.00
30.0 1.0 0.50 0.5 30.0 EX 5 A 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0
EX 6 A 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 7 A 45 30.0 1.00 30.0
1.0 0.50 0.5 30.0 EX 8 A 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 9 A
45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 10 A 45 30.0 1.00 30.0 1.0
0.50 0.5 30.0 EX 11 A 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 12 A
45 30.0 1.00 30.0 1.5 0.50 0.75 30.0 EX 13 A 45 30.0 1.00 30.0 2.0
0.50 1 30.0 EX 14 A 45 30.0 1.00 30.0 3.0 0.50 1.5 30.0 EX 15 A 45
30.0 1.00 30.0 2.0 0.50 1 30.0 EX 16 A 45 30.0 1.00 30.0 2.0 0.50 1
30.0 EX 17 A 45 30.0 1.00 30.0 2.0 0.50 1 30.0 EX 18 A 45 30.0 1.00
30.0 2.0 0.50 1 30.0 EX 19 A 45 35.0 1.00 35.0 2.0 0.25 0.5 18.0 EX
20 A 45 35.0 1.00 35.0 3.0 0.25 0.75 18.0 EX 21 A 45 30.0 1.00 30.0
2.0 0.50 1 30.0 EX 22 A 45 30.0 1.00 30.0 2.0 0.50 1 30.0 EX 23 B
45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 24 B 45 30.0 1.00 30.0 2.0
0.50 1 30.0 Treatment 1 and Treatment 2 Treatment 2 Post-treatment
Cathodic electrolysis Cathodic electrolysis treatment C2 treatment
Current Electric Current Electric application quantity Number of
Current application quantity time density times of Aqueous Temp.
density time density sec. C/dm.sup.2 treatment 2 solution .degree.
C. A/dm.sup.2 sec. C/dm.sup.2 EX 1 0.50 15.0 2 -- -- -- -- -- EX 2
0.30 9.0 3 -- -- -- -- -- EX 3 0.20 6.0 5 -- -- -- -- -- EX 4 0.10
3.0 7 -- -- -- -- -- EX 5 0.05 1.5 10 -- -- -- -- -- EX 6 0.25 7.5
2 E 40 0 1.00 0.0 EX 7 0.25 7.5 2 E 40 25 0.50 12.5 EX 8 0.30 9.0 3
E 40 25 0.50 12.5 EX 9 0.20 6.0 5 E 40 25 0.75 18.8 EX 10 0.10 3.0
7 E 40 25 0.75 18.8 EX 11 0.05 1.5 10 E 40 25 0.75 18.8 EX 12 0.50
15.0 2 -- -- -- -- -- EX 13 0.50 15.0 2 -- -- -- -- -- EX 14 0.50
15.0 2 -- -- -- -- -- EX 15 0.25 7.5 2 E 40 15 0.50 7.5 EX 16 0.25
7.5 2 E 40 20 0.50 10.0 EX 17 0.25 7.5 2 E 40 35 0.50 17.5 EX 18
0.25 7.5 2 E 40 15 1.50 22.5 EX 19 0.50 9.0 2 E 40 25 0.50 12.5 EX
20 0.50 9.0 2 E 40 25 0.50 12.5 EX 21 0.20 6.0 5 E 40 20 0.50 10.0
EX 22 0.10 3.0 7 E 40 20 0.50 10.0 EX 23 0.25 7.5 2 -- -- -- -- --
EX 24 0.25 7.5 2 -- -- -- -- -- Treatment 1 and Treatment 2
Treatment 1 Treatment 2 Cathodic electrolysis Anodic electrolysis
treatment C1 treatment A1 Cathodic electrolysis Current Electric
Current Electric treatment C2 Current application quantity Current
application quantity Current Aqueous Temp. density time density
density time density density solution .degree. C. A/dm.sup.2 sec.
C/dm.sup.2 A/dm.sup.2 sec. C/dm.sup.2 A/dm.sup.2 EX 25 B 45 30.0
1.00 30.0 1.0 0.50 0.5 30.0 EX 26 B 45 30.0 1.00 30.0 2.0 0.50 1
30.0 EX 27 B 45 30.0 1.00 30.0 2.0 0.50 1 30.0 EX 28 C 45 30.0 1.00
30.0 1.0 0.50 0.5 30.0 EX 29 C 45 30.0 1.00 30.0 2.0 0.50 1 30.0 EX
30 C 45 30.0 1.00 30.0 1.0 0.50 0.5 30.0 EX 31 C 45 30.0 1.00 30.0
2.0 0.50 1 30.0 EX 32 C 45 30.0 1.00 30.0 2.0 0.50 1 30.0 EX 33 D
45 35.0 1.00 35.0 1.0 0.50 0.5 30.0 EX 34 D 45 35.0 1.00 35.0 2.0
0.50 1 30.0 EX 35 D 45 35.0 1.00 35.0 1.0 0.50 0.5 30.0 EX 36 D 45
30.0 1.00 30.0 2.0 0.50 1 30.0 EX 37 D 45 30.0 1.00 30.0 2.0 0.50 1
30.0 EX 38 A 45 30.0 1.00 30.0 1.5 0.50 0.75 30.0 EX 39 A 45 30.0
1.00 30.0 1.5 1.00 1.5 30.0 EX 40 A 45 30.0 1.00 30.0 1.5 0.50 0.75
30.0 EX 41 A 45 30.0 1.00 30.0 1.5 1.00 1.5 30.0 EX 42 A 45 30.0
1.00 30.0 3.0 0.50 1.5 30.0 EX 43 A 45 30.0 1.20 36.0 4.5 0.50 2.25
30.0 EX 44 A 45 30.0 1.20 36.0 4.5 0.50 2.25 30.0 CE 1 A 45 30.0
1.00 30.0 2.0 0.50 1 30.0 CE 2 A 45 30.0 1.00 30.0 15.0 0.50 7.5
30.0 CE 3 A 45 30.0 1.00 30.0 2.0 0.50 1 30.0 Treatment 1 and
Treatment 2 Treatment 2 Post treatment Cathodic electrolysis
Cathodic electrolysis treatment C2 treatment Current Electric
Current Electric application quantity Number of Current application
quantity time density times of Aqueous Temp. density time density
sec. C/dm.sup.2 treatment 2 solution .degree. C. A/dm.sup.2 sec.
C/dm.sup.2 EX 25 0.25 7.5 2 E 40 20 0.50 10.0 EX 26 0.20 6.0 5 E 40
20 0.50 10.0 EX 27 0.10 3.0 7 E 40 20 0.50 10.0 EX 28 0.25 7.5 2 --
-- -- -- -- EX 29 0.25 7.5 2 -- -- -- -- -- EX 30 0.25 7.5 2 E 40
20 0.50 10.0 EX 31 0.20 6.0 5 E 40 20 0.50 10.0 EX 32 0.10 3.0 7 E
40 20 0.50 10.0 EX 33 0.25 7.5 2 -- -- -- -- -- EX 34 0.25 7.5 2 --
-- -- -- -- EX 35 0.25 7.5 2 E 40 20 0.50 10.0 EX 36 0.20 6.0 5 E
40 20 0.50 10.0 EX 37 0.10 3.0 7 E 40 20 0.50 10.0 EX 38 0.30 9.0 2
E 40 10 1.00 10.0 EX 39 0.30 9.0 2 E 40 10 1.00 10.0 EX 40 0.20 6.0
3 -- -- -- -- -- EX 41 0.20 6.0 3 E 40 10 1.00 10.0 EX 42 0.20 6.0
3 E 40 10 1.00 10.0 EX 43 0.20 6.0 3 -- -- -- -- -- EX 44 0.20 6.0
3 E 40 10 1.00 10.0 CE 1 0.50 15.0 1 -- -- -- -- -- CE 2 0.75 22.5
1 -- -- -- -- -- CE 3 0.50 15.0 1 E 40 20 0.50 10.0 EX: Example CE:
Comparative example
TABLE-US-00003 TABLE 3 Coating weight Cr metal layer structure Cr
Hydrated Base Granular protrusions Evaluation metal Cr oxide
portion Maximum Density Rust Rust layer layer Thickness diameter
Protrusions/ resistance resistance mg/m.sup.2 mg/m.sup.2 nm nm
.mu.m.sup.2 1 2 EX 1 137 6 11.5 130 70 A A EX 2 140 5 12.0 135 105
A A EX 3 145 5 12.0 120 500 A A EX 4 120 5 12.0 100 1150 A A EX 5
110 5 12.0 60 1500 A A EX 6 110 3 10.5 120 45 A A EX 7 115 20 10.5
120 45 A A EX 8 135 12 12.0 135 100 A A EX 9 145 18 12.0 120 500 A
A EX 10 120 19 12.0 100 1150 A A EX 11 110 18 12.0 50 1500 A A EX
12 135 6 10.5 120 55 A A EX 13 133 4 9.5 130 45 B B EX 14 130 5 8.0
145 35 C B EX 15 105 12 10.5 130 50 A B EX 16 105 16 11.0 130 53 A
B EX 17 105 22 11.5 130 55 A B EX 18 110 28 11.6 130 55 A B EX 19
140 16 12.0 180 50 A B EX 20 145 17 11.5 180 35 A B EX 21 125 16
11.5 120 480 A B EX 22 110 16 11.5 100 1100 A B EX 23 113 6 11.0
110 55 A A EX 24 100 5 9.5 130 40 B B Evaluation Primary Secondary
Under film Surface paint paint corrosion appearance Weldability
adhesion adhesion resistance EX 1 B A A B C EX 2 C A A B C EX 3 C A
A B C EX 4 C AA A B C EX 5 C AA A B C EX 6 B A A C C EX 7 B B A A A
EX 8 C B A B C EX 9 C A A A A EX 10 C AA A A A EX 11 C AA A A A EX
12 B A A B C EX 13 B A A C C EX 14 B A A C C EX 15 B B A A B EX 16
B B A A A EX 17 B C A A A EX 18 B C A A A EX 19 C B A A A EX 20 C B
A A A EX 21 C A A A A EX 22 C AA A A A EX 23 B A A B C EX 24 B A A
C C Coating weight Cr metal layer structure Cr Hydrated Base
Granular protrusions Evaluation metal Cr oxide portion Maximum
Density Rust Rust layer layer Thickness diameter Protrusions/
resistance resistance mg/m.sup.2 mg/m.sup.2 nm nm .mu.m.sup.2 1 2
EX 25 115 17 11.2 110 55 A A EX 26 115 16 11.5 100 600 A B EX 27
100 16 11.5 80 1200 A B EX 28 110 7 10.8 120 40 A A EX 29 108 4
10.0 135 25 B B EX 30 110 18 11.0 120 40 B A EX 31 110 17 11.0 110
550 A B EX 32 100 17 10.8 90 1150 A B EX 33 121 3 10.6 110 55 A A
EX 34 110 3 9.5 135 30 B B EX 35 122 17 10.9 110 55 A A EX 36 120
16 11.0 100 600 A B EX 37 110 16 10.8 80 1200 A B EX 38 120 15 11.0
130 90 A A EX 39 115 16 10.3 150 70 A A EX 40 125 5 10.5 110 120 B
A EX 41 120 15 9.8 120 100 B A EX 42 119 15 8.0 115 110 A B EX 43
110 5 9.0 190 70 C C EX 44 112 15 9.2 190 70 B C CE 1 105 5 11.0
110 18 A B CE 2 110 5 6.5 200 8 D E CE 3 125 18 11.3 110 19 A A
Evaluation Primary Secondary Under film Surface paint paint
corrosion appearance Weldability adhesion adhesion resistance EX 25
B A A A A EX 26 C A A A A EX 27 C AA A A A EX 28 B A A C C EX 29 B
A A C C EX 30 B A A A A EX 31 C A A A A EX 32 C AA A A A EX 33 B A
A B C EX 34 B A A C C EX 35 B A A A A EX 36 C A A A A EX 37 C AA A
A A EX 38 B B A A A EX 39 B B A A A EX 40 B A A C C EX 41 B B A C A
EX 42 C B A A A EX 43 C A A C C EX 44 C B A C A CE 1 B D A D C CE 2
C E A D C CE 3 B D A A A EX: Example CE: Comparative example
As is evident from the results shown in Table 3, it was revealed
that the tin mill black plates of Examples 1 to 44 were excellent
in weldability and also in rust resistance, under film corrosion
resistance and (primary and secondary) paint adhesions. In
contrast, the tin mill black plates of Comparative Examples 1 to 3
exhibited insufficient weldability, and some comparative examples
were insufficient in rust resistance and/or paint adhesion.
REFERENCE SIGNS LIST
1: tin mill black plate
2: steel sheet
3: chromium metal layer
3a: base portion
3b: granular protrusion
4: hydrated chromium oxide layer
* * * * *